The present invention relates to nose sprockets for chain saws, and to a method of making such a nose sprocket.
Thin nose sprockets have long been used to carry a saw chain around the nose of a guide bar. The sprockets carry the chain without friction against the guide bar edges, resulting in less wear and less power requirement.
In vehicle-mounted chain saws the chain is subjected to very high velocity and tensile force. The engine power is much higher than in manual chain saws and the operator has no direct view of the cutting area. If a tree trunk is leaning when sawn through, the saw chain and guide bar may be compressed so hard that the chain of a manual chain saw stops, but the chain of a vehicle-mounted saw may still keep running. This will cause damage by overheating the nose sprocket until it becomes buckled and skewed, followed by local welding and seizure.
Several guide bar and sprocket designs have been suggested to lessen the risk of such damage, such as increasing the space between the sprocket and the guide bar side plates, or pressure-lubricating the sprocket bearing with an excess of lubricant enough to lubricate the sprocket sides. This has at least created a possibility to continue sawing with a slightly deformed sprocket, but has not solved the problem of overheating during the initial compression stage.